Vegetable oils have a variety of uses as food constituents and cooking aids, and are typically refined before use. Crude vegetable oils are generally refined to remove free fatty acids and other undesirable components by one of two broad methods, chemical and physical refining. Chemical refining is most commonly accomplished by the use of caustic refining compounds, such as by treating a crude oil with a sodium hydroxide solution. Physical refining is commonly accomplished by distillative neutralization, in which the free fatty acids are removed by water vapor.
Many vegetable oils degrade over time when left in contact with oxygen. Degradation can be slowed by adding one or more antioxidants to the oil. Common synthetic antioxidants include butylated hydroxytoulene (BHT), butylated hydroxyanisole, tertiary butylated hydroquinone, and propyl gallate. However, many consumers prefer natural antioxidants, such as tocopherals (vitamin E), tocotrienols, ferulates, e.g., gamma oryzanol, and sulfur-containing amino acids. These natural antioxidants are present in many crude oils, but are typically removed along with the free fatty acids during standard refining methods. Tocotrienols, ferulate esters of triterpene alcohols, e.g., gamma oryzanol, and ferulates are unsaponifiables with cholesterol-lowering properties.